Phenol and methyl ethyl ketone are important products in the chemical industry. For example, phenol is useful in the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, alkyl phenols, and plasticizers, whereas methyl ethyl ketone can be used as a lacquer, a solvent and for dewaxing of lubricating oils.
The most common route for the production of methyl ethyl ketone is by dehydrogenation of sec-butyl alcohol (SBA), with the alcohol being produced by the acid-catalyzed hydration of butenes. For example, commercial scale SBA manufacture by reaction of butylene with sulfuric acid has been accomplished for many years via gas/liquid extraction.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene relative to that for butenes is likely to increase, due to a developing shortage of propylene. Thus, a process that uses butenes instead of propylene as feed and coproduces methyl ethyl ketone rather than acetone may be an attractive alternative route to the production of phenol.
It is known that phenol and methyl ethyl ketone can be co-produced by a variation of the Hock process in which sec-butylbenzene is oxidized to obtain sec-butylbenzene hydroperoxide and the peroxide decomposed to the desired phenol and methyl ethyl ketone. An overview of such a process is described in pages 113-121, 261 and 263 of Process Economics Report No. 22B entitled “Phenol,” published by the Stanford Research Institute in December 1977.
Sec-butylbenzene can be produced by alkylating benzene with n-butenes over an acid catalyst. The chemistry is very similar to ethylbenzene and cumene production. However, as the carbon number of the alkylating agent increases, the number of product isomers also increases. For example, ethylbenzene has one isomer, propylbenzene has two isomers (cumene and n-propylbenzene), and butylbenzene has four isomers (n-, iso-, sec-, and t-butylbenzene). For sec-butylbenzene production, it is important to minimize n-, iso-, t-butylbenzene, and phenylbutenes by-product formation. These by-products, especially iso-butylbenzene, have boiling points very close to sec-butylbenzene and hence are difficult to separate from sec-butylbenzene by distillation (see table below).
ButylbenzeneBoiling Point, ° C.t-Butylbenzene169i-Butylbenzene171s-Butylbenzene173n-Butylbenzene183
Moreover, isobutylbenzene and tert-butylbenzene are known to be inhibitors to the oxidation of sec-butylbenzene to the corresponding hydroperoxide, a necessary next step for the production of methyl ethyl ketone and phenol.
It is also desirable to reduce other by-products such as butene oligomers, dibutylbenzenes and tributylbenzenes. These by-products consume butene and benzene feed and compromise sec-butylbenzene selectivity. The olefinic butene oligomers can also have an inhibiting effect on sec-butylbenzene oxidation rates.
Moreover, although sec-butylbenzene production can be maximized by using a pure n-butene feed, it is desirable to employ more economical butene feeds, such as Raffinate-2. A typical Raffinate-2 contains 0-1% butadiene and 0-5% isobutene. With this increased isobutene in the feed, a higher t-butylbenzene make is expected, which further increases the importance of the sec-butylbenzene selectivity of the catalyst. In our International Application No. PCT/EP2005/008557, filed Aug. 5, 2005, we have described an integrated process for producing phenol and methyl ethyl ketone, the process comprising (a) contacting a feed comprising benzene and a C4 alkylating agent under alkylation conditions with a catalyst comprising zeolite beta or an MCM-22 family zeolite to produce an alkylation effluent comprising sec-butylbenzene; (b) oxidizing the sec-butylbenzene to produce a hydroperoxide; and then (c) cleaving the hydroperoxide to produce phenol and methyl ethyl ketone. The alkylation conditions include a temperature of about 60° C. to about 260° C., for example about 100° C. to about 200° C., with all the Examples being conducted at 160° C.
In accordance with the present invention, surprisingly it has now been found that if the alkylation process described in our International Application No. PCT/EP2005/008557 is conducted with the temperature controlled within narrowly defined limits of about 110° C. to about 150° C., then the selectivity to sec-butylbenzene is significantly increased over operation at higher temperatures without excessive loss in the activity of the catalyst. Since the alkylation product is substantially free of isobutylbenzene and tert-butylbenzene, it is an attractive feed for use in the Hock process to produce phenol and methyl ethyl ketone. It is known from, for example, U.S. Pat. No. 4,992,606 that MCM-22 is an effective catalyst for alkylation of aromatic compounds, such as benzene, with alkylating agents, such as olefins, having from 1 to 5 carbon atoms over a wide range of temperatures from about 0° C. to about 500° C., preferably from about 50° C. and about 250° C. Similar disclosures are contained in U.S. Pat. Nos. 5,371,310 and 5,557,024 but where the zeolite is MCM-49 and MCM-56 respectively. However, there is no disclosure or suggestion in these references that MCM-22, MCM-49 or MCM-56 should be unusually selective to sec-butylbenzene in the alkylation of benzene with a C4 alkylating agent, particularly when the alkylation process is conducted at a temperature of about 110° C. to about 150° C.